The invention relates to routers that are used on computer networks.
A router is a device that is used to interconnect Local Area Networks (LANs) and stations to form large networks. As networks grow in speed to 100 Mbit/sec and higher, the performance of routers has become an important issue. Because the performance of routers is often limited by the fixed overhead of processing the header of a packet, the performance of a router is often measured in packets/second. Currently, there are a few high-end routers with a performance of 60-80,000 packets/second. Depending on the average size of the packets being forwarded, this translates into a forwarding rate of between 16 Mbit/sec (using 32 byte packets) and 100 mbit/sec (using 256 byte packets).
Currently, the next milestone that most high-end router vendors are aiming for is to exhibit a router that can forward 100,000 packets/second. But one major reason why the forwarding performance of many high speed routers cannot reach 100,000 packets per second is that performance is limited by the speed of the router's internal backplane bus. Their performance, however, though limited by the speed of the backplane, is quite adequate for connecting low speed (10 Mbit/sec or less) lines.
Recently crossbar switches have appeared in the marketplace (e.g. the GIGAswitch from Digital Equipment Corporation) that are able to transfer packets at a rate of 1/2 million packets per second. The GIGAswitch, for example, has 22 ports that can connect 22 lines of 100 Mbit/sec or greater. These include FDDI LANs as well as ATM, SONET, and SMDS lines. The GIGAswitch also has a feature called "hunt groups" by which several ports can be grouped together to form a logical port (for further details see U.S. patent application, Ser. No. 07/542,856 now issued as Pat. No. 5,265,257, on Nov. 23, 1993, entitled Fast Arbiter Having Easy Scaling for Large Numbers of Requesters, Large Numbers of Resource Types with Multiple Instances of Each Type, and Selectable Queuing Disciplines, incorporated herein by reference). Packets sent to a logical port are sent by the switch to any of the physical ports that constitute the hunt group. Thus, any packets sent from the high speed lines to the hunt group are distributed among the physical ports according to a load balancing algorithm inside the switch. The result is increased bandwidth communication to the hunt group.
Such switches, however, do not have ability to be a router.